This is the story about how scientists working in a small outpost in central Ontario found out about acid rain — and how their discoveries changed the world. Thanks to the efforts of scientists like Wolfgang Scheider, Norman Yan and Peter Dillon, biologists employed by the Ontario government in the 1970s, we discovered how acid rain was affecting our environment, where it came from, and what could be done to control it. Today, people in Ontario, across Canada and around the world are familiar with the efforts to control emissions from industry and vehicles. These emissions caused rain and snow to turn acidic and affected the composition of lakes and rivers across North America. Both air quality and the acidic/alkaline balance in Ontario’s waterways have greatly improved thanks to emission control programs such as Countdown Acid Rain, the province’s aggressive regulations that curbed sulphur dioxide and nitrogen oxide emissions from industries and electric power plants. Many people are also familiar with the political battles that that took place to bring these improvements into place. The battles involved environmentalists, Ontario and other provincial governments, the federal government, the United States and the international community. The discovery of acid rain   The story of the scientific research into acid rain began in 1966. A University of Toronto biologist named Harold Harvey and his student Dick Beamish introduced 4,000 pink salmon into Lumsden Lake in Killarney Provincial Park, southwest of Sudbury, to see how fish stocks could survive and thrive in the area. The water in Lumsden Lake and other lakes nearby was remarkably clear. It was also downwind from sulphur dioxide emissions that blew from the huge smokestack at (then) Inco Ltd.’s Sudbury nickel smelter. Elsewhere, scientists Gene Likens in Hubbard Brook, New Hampshire and Svandt Oden in Sweden were also doing pioneering work in acid rain. A year after introducing the fish into Lumsden Lake, Harvey went back, but could not find a single fish he had left there. He came back year after year, and there were still no fish. In the late 1960s and early 70s, Harvey told his students at the university about his observations . Scheider, one of his biology students, remembers this was the first time he has heard anyone make the connection between long-range air pollution and changes to the water in lakes and rivers. At first people thought that the rising acid levels in Ontario lakes was a local problem. Gradually, through the efforts of scientists like Scheider, Yan and Dillon, they learned that it was due to the “long-range transport of atmospheric pollutants”, or LRTAP. As measurement technology and techniques improved, they could trace the sources of the pollutants more accurately, and they found that in many cases these materials came from airborne particles from smokestacks not just in nearby Sudbury, but from hundreds of kilometres away in southern Ontario and the U.S. Midwest. The media began to call this pollution acid rain, and the name stuck among scientists and the public. In the 1970s, Scheider, Yan and Dillon took to the wilderness to find out more about it. They headed to set up base in Dorset, Ontario, a city in scenic Muskoka, near Algonquin Provincial Park. There, they performed intensive site and lab work on lakes such as Plastic Lake in the area. What the scientists learned The Dorset-based scientists were able to show how pH levels in Ontario lakes were increasing drastically; within years, they could become tens and hundreds of times more acidic than they had been in the past. The scientists could also trace where the acid rain was coming from. In the Dorset area, 75 per cent of it came from the southwest, meaning it originated in the midwestern U.S., largely from industries and coal-burning power plants. At first, it was thought that the solution to neutralizing acidic lakes was simply to put more lime into the water. Indeed, this is what the scientists’ counterparts were doing in Sweden, and for a time a part of the three men’s work was to lug 36-kg (80 lbs.) bags of lime by the truckload to lakes in the Sudbury area, pick them up and dump them in. It was tiring, and futile. Soon, scientists and officials realized that the problem was bigger and more widespread than something that could be solved with bags of lime. There were too many lakes and rivers; the acidic lakes were not something that could be solved by a few people hauling around bags of lime. The pioneering scientific work of Scheider, Yan and Dillon and other Ontario scientists led to the political and environmentalist action that became Countdown Acid Rain [Ontario’s acid rain reduction program for industry and utilities] and brought down emission levels. Their studies of acid rain even led to wider research into more complex environmental problems, leading other scientists to look more deeply into toxic chemicals in the atmosphere and climate change. Today, though acid rain is still with us, the levels are much less than in the 1970s. Ontario is phasing out coal-fired power plants, and the emission levels of Inco in Sudbury, one of the major polluters in Ontario (now owned by Vale Corp.), are down by more than 90 per cent. This is a success story that we owe to these scientists. As Wolfgang Scheider says: “The story has many lessons for environmentalists today, including the length of time it may take to improve the quality of the environment due to earlier damages. We still have a way to go toward recovery in some lakes across Ontario. However, as this story demonstrates, concerted action by governments, industries and others, with support from the public can be successful.”